Disturbances due to

1
Disturbances due to high frequency signals
(above 2 kHz)
Martin Lundmark EMC on Site martin.lundmark_at_ltu.s
e
2
OUTLINE

1. BACKGROUND
2. CONDUCTIVE AND RADIATED EMISSION IN A THREE-PHASE
   GRID
3. ORIGIN OF CONDUCTIVE HIGH-FREQUENCY LEAKAGE
   CURRENT
4. MEASUREMENTS
5. CONCLUSION

3

• BACKGROUND
• Sign of HF-harmonics
• PWM motor drives - motor bearing currents
• TV and audio studios - disturbances
• Power Line Communication - signal interference
• Distribution transformers - damage
• Power supply units - damage
• Cable and cable termination - damage
• Electronic office equipment - malfunction
• Fluorescent lights - league currents

4

• BACKGROUND
• CHANGING CIRCUMSTANCES IN POWER LOADS
• The use of power electronics
• Faster changes in loads than in the power grid
• AND IN COMMUNICATION
• The changes from analogue to digital
  communications technique
• The radiated emission of electronic equipment is
  limited with respect to analog radio
  communications services

5
BACKGROUND The changes from analogue to
digital communications technique
6
CONDUCTIVE AND RADIATED EMISSION IN A
THREE-PHASE GRID
7
CONDUCTIVE EMISSION IN A THREE-PHASE GRID
8
ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT
Symmetrical load current in a three phase system
9
ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT
Symmetrical load current, including harmonics,
in a three phase system
10
ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT
Symmetrical load current, including HF-
harmonics, in a three phase system
11
ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT
Symmetrical load current, including HF-
harmonics, in a three phase system
1
1
A detail of the left graph shows the damped peak
having about a 156 microsecond period time, a
frequency close to 6.4 kHz.
A 2 kHz high-pass filter used on the simulated
neutral current from HF fluorescent lamps in
three-phase connection
1
12
Symmetrical load current, including HF-
harmonics, in a three phase system

lt2 kHz
gt2 kHz
Neutral current (RMS) when increasing the numbers
of three-phase connected HF-fluorescent lamps,
unfiltered upper left, 2 kHz high-pass filter
down left. To the right- the neutral current
shown on the left is divided by the number of
three-phase connected groups of HF-fluorescent
lamps.
13
Symmetrical load current, including HF-
harmonics, in a three phase system
1
Highest peak value in neutral current above 2 kHz
when increasing the numbers of three-phase
connected HF fluorescent lamps, to the left. To
the right, the peak value is divided by the
number of three-phase connected groups of HF
fluorescent lamps.
14
Symmetrical load current, including HF-
harmonics, in a three phase system
Z
100 m
Z R jX
The impedance for 2.5 mm 2 Cu wire with a length
of 100 m upper line, 30 m middle line and 1 m
lower line.
1 m
30 m
15
ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT
Symmetrical load current, including HF-
harmonics, in a three phase system
Calculations on the neutral peak voltage with
increasing numbers of HF-fluorescent lamps with
(upper line) and with only the wire resistance
(lower line). Z R jX, for 2.5 mm2 Cu wire
with a length of 30 m
16
ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT
17
MEASUREMENTS
18
Communications failures on a specific
communication line in a server room powered by a
50 kVA uninterruptible power supply
P-N
N-PE
P-PE
19
MEASUREMENTS
A- building, in the office part of the LTU
Skellefteå Campus.
20
MEASUREMENTS
D-building, first floor, adjacent to room 3045.
21
MEASUREMENTS
A- building
D-building, first floor
22

• CONCLUSION
• It is possible to find HF- harmonics, almost
  everywhere in power grids.
• The origin to the HF- harmonics is finding in
  power electronics in domestic, commercial and
  industrial equipment.
• The number of emitting devices is growing
  significantly.
• Literature describes interference on electronic
  office equipment, in TV and audio studios and in
  power grid using power line communication due to
  HF- harmonics, to give some examples.
• Literature also describes damage in distribution
  transformers, cable and cable termination and in
  motor bearings due to HF- harmonics.
• While the symmetrical fundamental frequency
  current is cancelled and the zero-sequence
  harmonics is summarized in the neutral wire the
  HF- harmonic current increased when the number of
  loads symmetrically increased in the three
  phases, and there was almost no cancellation.
• Adding the effect of increasing impedance in
  wires resulting from increasing frequency, one
  origin of conductive high-frequency leakage
  current in the grid is shown.

23
THANK YOU